HAVANA (AP) - Retired leader Fidel Castro broke nearly a week of silence since the death of friend and ally Hugo Chavez, saying Monday that Cuba has lost its "best friend" with the late Venezuelan president's passing.

In an article published on the front page of Communist Party newspaper Granma, Castro said that while it had been clear that Chavez's life was threatened by a recurring cancer affliction that prompted four surgeries, word of his death on March 5 nonetheless came as a bitter shock.

"The best friend the Cuban people have had in the course of their history passed away. ... Although we knew of his critical state of health, the news was a strong blow," Castro wrote.

The 86-year-old Castro, who has been out of power since a near-fatal intestinal ailment forced him from office in 2006, has ceased penning his once-regular opinion pieces, known as "Reflections."

Last October, amid the latest round of rumors about his own health, Castro explained that he decided to do so not because he was ill but because they were taking up valuable space in state media that was needed for other purposes.

In life, Chavez often referred to Castro as a father figure, mentor and close friend, and after he first won election in 1998, Havana and Caracas grew increasingly close.

Chavez supplied Cuba with billions of dollars in subsidized oil to help prop up the island's listing economy, while Havana sent tens of thousands of doctors, teachers, sports trainers and political advisers to work in Venezuela.

Venezuela has become Cuba's No. 1 trading partner.

Following Chavez's latest surgery in Havana in December, Castro said he checked in on the Venezuelan president's health daily.

On Monday, he recalled that Chavez once invited him to go on a riverboat excursion in Venezuela once the two leaders'"revolutionary task" was finished.

Invoking Cuban independence hero Jose Marti and 19th century Venezuelan liberator Simon Bolivar, Castro said it had been an honor to have been Chavez's ally.

"Not even he suspected how great he was," Castro wrote. "Onward to victory always, unforgettable friend!"